1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices including thin film transistors, light-emitting elements, passive elements, and the like. Furthermore, the present invention relates to electro-optical devices represented by liquid crystal display panels, light-emitting display devices that have light-emitting elements, and electronic devices in which IC tags, by which information can be transmitted and received wirelessly, are mounted as components.
It is to be noted that “semiconductor device” in the present specification refers to a general device that can function as a semiconductor device using semiconductor characteristics, and electro-optical devices, light-emitting devices, semiconductor circuits, IC tags, and electronic devices can all be considered semiconductor devices.
2. Description of the Related Art
In recent years, technology that is used to form thin film transistors using semiconductor thin films (with thicknesses of from several nanometers to several hundreds of nanometers, approximately) that are formed over substrates that have an insulating surface has been attracting attention. Thin film transistors are applied to a wide range of electronic devices like ICs and electro-optical devices, and prompt development of thin film transistors that are to be used as switching elements in image display devices, in particular, is being pushed.
With applications that use these kinds of image display devices, a variety of things are being expected, and use in portable devices, in particular, is attracting attention. Glass substrates and quartz substrates are often used in image display devices; however, there are disadvantages to using glass substrates and quartz substrates in that they are easily breakable as well as heavy. Furthermore, increasing the size of glass substrates and quartz substrates, such as for mass production, is difficult, and glass substrates and quartz substrates are thus not suitable for mass production. For these reasons, forming thin film transistors over flexible substrates, typically, flexible plastic films, is being attempted.
Thus, technology in which semiconductor elements, including thin film transistors, that are formed over glass substrates are separated from the glass substrates and transferred to other substrates, for example, to plastic films or the like, has been proposed.
The present applicant proposed the separation and transfer technique that is disclosed in Patent Reference Document 1 and Patent Reference Document 2. In Patent Reference Document 1, a separation technique by which a silicon oxide film that is to be used as a peeling layer is removed by wet etching is disclosed. In addition, in Patent Reference Document 2, a separation technique by which a silicon film that is to be used as a peeling layer is removed by dry etching is disclosed.
Furthermore, the present applicant proposed the separation and transfer technique that is disclosed in Patent Reference Document 3. In Patent Reference Document 3, a technique where a metal (Ti, Al, Ta, W, Mo, Cu, Cr, Nd, Fe, Ni, Co, Ru, Rh, Pd, Os, or Ir) layer is formed over a substrate, an oxide layer is formed and stacked thereover, a metal oxide layer of the metal layer is formed in the interface between the metal layer and the oxide layer, and separation from the substrate is performed during a subsequent step using this metal oxide layer is disclosed.    Patent Reference Document 1: Japanese Published Patent Application No. H8-288522    Patent Reference Document 2: Japanese Published Patent Application No. H8-250745    Patent Reference Document 3: Japanese Published Patent Application No. 2003-174153